1. Field of Technology
The present invention generally relates to a magnetic tape recording and/or reproducing apparatus and, more particularly, to an improvement in noiseless reproduction of a slow motion effect in the magnetic tape recording and/or reproducing apparatus.
2. Description of the Prior Art
A video tape recording and/or reproducing apparatus, or a video tape player for short, having a capability of creating a plurality of altered motion effects including, in addition to a normal picture motion effect, a slow motion effect, a stop motion effect, a reverse motion effect and so on is well known in the art and is currently widely used in the ordinary home.
An example of prior art video tape player and particularly the circuit arrangement employed therein, in connection with the slow motion reproduction of information from an information carrier medium, (that is, a length of magnetic tape,) will be discussed with reference to FIGS. 1 and 2 of the accompanying drawings.
FIG. 1 illustrates the enlarged segment of the magnetic tape having field tracks recorded thereon and the circuit arrangement of the prior art video tape player which is associated with the slow motion reproduction of the information. FIG. 2 illustrates waveforms of various signals appearing in the prior art video tape player which are shown in a timing relationship.
Referring first to FIG. 1, the prior art video tape player, generally identified by 10, comprises a tape guide cylinder around which a length of magnetic tape 1, running from a supply reel 14 towards a take-up reel 15, is movably turned through a predetermined angle, for example, 180.degree.. As is well known to those skilled in the art, while the supply and take-up reels 14 and 15 are accommodated within a standardized cassette in spaced relationship, with opposite ends of the magnetic tape 1 secured respectively thereto, the tape guide cylinder is comprised of a stationary drum and a rotary drum 11 supported above the stationary drum in coaxial relation therewith and for rotation in one direction relative thereto. The rotary drum 11 is drivingly coupled with a drive motor 20 and has a plurality of, for example, two, transducing head assemblies 12 and 13 carried thereby for rotation together therewith. The head assemblies 12 and 13 are spaced a predetermined angle, for example, 180.degree., from each other in a direction circumferentially of the rotary drum 11. Each of the transducing head assemblies 12 and 13 is concurrently utilized for recording and reproducing information on and from the magnetic tape, respectively, at a time in a conventional manner.
The length of magnetic tape 1 is moved along a predetermined operative path between the supply reel 14 and the take-up reel 15 by any conventional means which, in the illustrated instance, consists of a rotating capstan 16 drivingly coupled with a capstan motor 25, against which capstan 16 is pulled the magnetic tape 1 by a pinch roller 17. Adjacent a portion of the operative path for the travel of the magnetic tape 1, between the tape guide cylinder and the capstan 16, there is disposed a control signal recording and reproducing head 18 for recording or reproducing a control signal c on or from a control track 4 on the magnetic tape 1. Control signal c is a reference signal used to control the transport of the magnetic tape 1 from the supply reel 14 onto the take-up reel 15. The control signal recording and reproducing head 18, referred to above, is hereinafter referred to as "CTL head" for the sake of brevity.
As best shown in the upper portion of FIG. 1, a segment of the magnetic tape 1 is shown to have a number of information recorded tracks track 2 and 3 thereon, together with arrows x and y which respectively illustrate the direction of movement of the magnetic tape 1 from the supply reel 14 onto the take-up reel 15 around the tape guide cylinder, and the direction of scan of the transducing head assemblies 12 and 13 relative to the magnetic tape 1. As a matter of design practice in the known helical scan video tape player, when moving past the tape guide cylinder, the magnetic tape 1 extends generally slantwise relative to the plane of rotation of the transducing head assemblies 12 and 13; The and recorded tracks 2 and 3 are inclined at a predetermined angle relative to the longitudinal or lengthwise direction of the magnetic tape 1. More specifically, the beginning of one field signal recorded on each track 2 and 3 is located adjacent a lower side edge of the length of magnetic tape 1 and also adjacent to the control track 4. The end of one such field signal recorded on the respective track 2 and 3 is located adjacent an upper side edge of the same length of magnetic tape 1, with a substantially intermediate portion thereof extending at that predetermined angle relative to the lengthwise direction of the magnetic tape 1.
Where the helical scan video tape player 10 is so designed so as to operate under a VHS (Video Home System) scheme, one of a plurality of recorded tracks on the length of magnetic tape 1, identified by A, is laid down by a magnetic recording and/or reproducing head having a head gap of an azimuth angle of 6.degree.. The next adjacent trailing recorded track, identified by B, on the same length of magnetic tape 1, is laid down by a magnetic recording and/or reproducing head having a head gap of an azimuth angle of -6.degree.. The control c is recorded on the control track 4, and the distance between the position of the control signal c on the control track 4 and the position of the length of magnetic tape 1 where the end of the recorded track B is located, is referred to as "X value"; The X value is fixed at 79.244mm according to the VHS system norm.
Video field signals picked up respectively by the magnetic head assemblies 12 and 13, which are alternately switched on and off in a manner well known to those skilled in the art, are fed to a rotary transformer 30, comprised of windings, carried by the rotary drum 11, and windings fixedly carried by the apparatus, and then, after having been amplified by respective video signal amplifiers 31 and 32, to a head switching circuit 33. These amplifiers 31 and 32 and the circuit 33 constitute a reproducing circuit operable in interlace an output signal from each of the head assemblies for producing a video signal f.
On the other hand, to this head switching circuit 33 is applied a head switching signal a. This signal has been generated from head switching signal detecting heads 22 and 23, spaced a predetermined angle, for example, 180.degree., from each other in a direction circumferentially of the drum drive motor 20 and operable in cooperation with a head switching signal generating element 21 secured to the drum drive motor 20 for rotation together therewith. The signal has subsequently been amplified and wave-shaped by a head switching signal generator 24. Accordingly, the head switching circuit 33 generates alternately reproduced signals which are picked up initially by the magnetic head assemblies 12 and 13 and then by scanning the recorded tracks 2 and 3. The head switching signal a is, as shown by (a) in FIG. 2, so generated from the head switching signal generator 24 that, when it is in an ON state, the magnetic head assembly 12 can be brought into operation. However when it is in an OFF state, the magnetic head assembly 13 can be brought into operation.
A reproduced video signal f, outputted from the head switching circuit 33, is subjected to a signal processing technique, such as amplification, detection, frequency conversion and other. This is performed in a signal processing circuit 34 and is then supplied to a quasi-vertical synchronizing signal adding circuit 35 from which a reproduced video signal 36 is outputted. The head switching signal a, is processed in the quasi-vertical synchronizing signal generator 46 to produce a quasi-vertical synchronizing signal b, the waveform of which is shown by (b) in FIG. 2. This quasi-vertical synchronizing signal b is, in the event that the vertical synchronizing signal is not properly reproduced because of the presence of noises during the playback of a stop motion picture or the like, applied to the quasi-vertical synchronizing signal adding circuit 35 shown in FIG. 1 where it is added to the reproduced video signal 36. According to the VHS system, since the vertical synchronizing signal is located at a position which has passed 6.5 times the cycle of the horizontal synchronizing signal subsequent to the switching of the head assemblies, a delay time between the set-up and set-down of the head switching signal a, and the quasi-vertical synchronizing signal b, is equally selected.
On the other hand, both the head switching signal a, and the control signal c, picked up by the CTL head 18, are supplied to a capstan control circuit 26. From there a voltage signal proportional to the difference in phase therebetween is outputted. The voltage signal is in turn applied to a capstan motor drive circuit 27 operable to control the rotational speed, i.e., the number of revolution, of the capstan drive motor 25 in dependence on the voltage signal applied thereto. Accordingly, during the normal picture reproduction of video information, the head switching signal a, and the control signal c, have a predetermined phase relationship with each other, whereby the magnetic head assemblies 12 and 13 can properly scan the recorded tracks on the length of magnetic tape 1. The stop motion effect can be accomplished when the transport of the length of magnetic tape 1 is stopped.
In FIG. 1, reference numeral 40 represents a slow motion mode selector switch adapted to be manipulated by a viewer of the video tape player when he or she wishes to view a slowed-down reproduction of video information; Reference numeral 41 represents a delay circuit operable to delay the control signal c, for a predetermined delay time. Reference numeral 41a represents a delay time adjustment operable to adjust the length of delay time t. Reference numeral 42 represents a tape transport control circuit. Reference numeral 45 represents a head switching signal counting circuit. The combination of all of these circuit components constitute a slow motion control device.
Hereinafter, the slow motion reproduction accomplished in the prior art video tape player of the construction described above will be discussed. As it is well known to those skilled in the art, the slow motion reproduction can be accomplished by alternately performing a still picture reproduction and a normal picture reproduction in a manner well known to those skilled in the art.
The relationship between noises produced in the television raster during the still picture reproduction, and the position at which the length of magnetic tape 1 is stopped, will be described with particular reference to FIGS. 3 and 4. During the still picture reproduction, the head assemblies 12 and 13 are employed with each having their respective head gaps laid at the same azimuth angle. Because of this, the head assembly 13 has two magnetic heads, each having their head gaps laid at different azimuth angles. These are selectively utilized during the normal picture reproduction and during the still picture reproduction, one at a time. An electric circuit is necessary to selectively bring the magnetic heads into operation, one at a time, which is not shown in FIG. 1. Assuming that the relationship between the recorded tracks on the length of magnetic tape 1, and the trace 5, of movement of the magnetic head assembly at the time the transport of the magnetic tape 1 is stopped, is such as shown in FIG. 3a. The recorded track actually reproduced, that is, scanned, will be narrow such as represented by hatched areas in FIG. 3a . This is because the azimuth angle of the track A, and the azimuth angles of the respective head gaps of the magnetic head assemblies 12 and 13, match with each other. Therefore, the reproduced video signal f, will be partially dropped out as shown by (f) in FIG. 2. As a result thereof, the drop-out portion of the reproduced video signal when viewed on the screen of a cathode ray tube, represents noise bands appearing in the stop motion picture. The picture will not be properly reproduced.
On the other hand, where the relationship between the recorded track on the length of magnetic tape 1 and the trace 5 of movement of the magnetic head assembly is such as shown in FIG. 3b, the recorded track actually reproduced will be large such as shown by a hatched area in FIG. 3b. This is because the azimuth angle of the track A and the azimuth angles of the respective head gaps of the magnetic head assemblies 12 and 13 match with each other. Therefore, the reproduced video signal f1 will be such as shown by (f1) in FIG. 2. No band noise will appear on the screen of the cathode ray tube.
The manner in which the magnetic tape 1 is moved and stopped during the slow motion reproduction will now be described with reference to FIGS. 1 to 3. When the slow motion selector switch 40 is closed, a slow motion command signal is applied to a tape transport control circuit 42. The tape transport control circuit 42 generates a capstan stop signal d, (the waveform of which is shown by (d) in FIG. 2) to the capstan motor drive circuit 27. This operates to stop the capstan drive motor 25 in response to the capstan stop signal d. A still picture is hereinabove described, which is reproduced at the time the capstan drive motor 25 is brought to a halt.
The head switching signal counting circuit 45 then starts its counting operation. It counts the number of head switching signals a generated subsequent to the interruption of movement of the magnetic tape 1. It further generates a signal e when a predetermined number of the head switching signals a appropriate for a particular slow motion reproduction have been counted. For example, six signals are used in the case where the slow motion reproduction takes place while the magnetic tape 1 is transported at a velocity one sixth of that during the normal picture reproduction. The signal e is, in turn, applied to the tape transport control circuit 42 which then generates a capstan drive signal d1 to the capstan motor drive circuit 27 to drive the capstan drive motor 25. Simultaneously therewith, the delay circuit 41 is brought into operation in response to the signal e to delay the control signal c for a predetermined time tt, as shown in the waveform (d) in FIG. 2. After which, a delayed control signal cc is applied from the delay circuit 41 to the tape transport control circuit 42. In response to the delayed control signal cc, the tape transport control circuit 42 applies a capstan stop signal d, (the waveform of which is shown by (d) in FIG. 2), to cause the capstan motor drive circuit 27 to bring the capstan drive motor 25 to a halt.
Subsequent to the interruption of the movement of the magnetic tape 1, the head switching signal counting circuit 45 starts its counting operation. It counts the number of the head switching signals a applied thereto, and generates the signal e when the predetermined number (that is, six in the instance now under discussion,) of the head switching signals a are counted then signal e is applied to the tape transport control circuit 42. The tape transport control circuit 42 then generates the capstan drive signal d1 which is applied to the capstan motor drive circuit 27 causing the capstan drive motor 25 to be driven. By alternately driving and stopping the magnetic tape 1 through a number of cycles in the manner described hereinabove, the slow motion reproduction can be accomplished.
During this slow motion reproduction, in the event that noises appear on the picture being reproduced, it is customary for the viewer or operator of the video tape player to manipulate the adjustment 41a to adjust the delay time tt to a value t1 (shown in the waveform (d) in FIG. 2). Thus, the appearance of the noises can be substantially eliminated. Specifically, if the delay time tt is adjusted to the value t1 by manipulating the adjustment 41a, the position at which the drop-out portion of the reproduced video signal occurs can, during the still picture reproduction, be brought into alignment with the position where the switching of the head assemblies takes place. That is, it can be synchronized with a vertical synchronizing signal. Therefore, no noise appears on the picture being reproduced. At the same time, the speed of movement of the magnetic tape 1 past the tape guide cylinder is controlled to a predetermined value at which no noise occurs in the picture being reproduced on the cathode ray tube. This is provided, however, the head assemblies scan the position where no noise occurs during the stop motion reproduction, so that the noiseless slow motion reproduction can be accomplished.
However, in the prior art video tape player of the construction hereinabove described, the time which is passed until the capstan drive motor 25 is brought to a halt varies from one product to another. Therefore, the relationship in timing between the head switching signal a or the control signal C and the time at which the capstan 16 is brought to a halt, (that is, the delay time t of the delay circuit 41), has been required to be manually adjusted for each capstan drive motor 25 used in the respective video tape player. Moreover, since in general the X value tends to fluctuate often, (even where the X value differs between the video tape player used to make a recording of information on the magnetic tape and that used to make a reproduction of the recorded magnetic tape). The occasional manual adjustment of the delay time t has been required.
In view of the foregoing, not only are generally complicated procedures required to handle the prior art video tape player, but also the precise adjustment of the delay time is difficult to achieve.